Spectacle lenses (to be also referred to as lenses hereinafter) include different types such as a single-vision lens, a multifocal lens, and a progressive multifocal lens, and their diameters, outer diameters, lens powers, and the like differ from one lens type to another. Hence, a large number of types of lenses must be fabricated.
Conventionally, edging of such lenses is performed in accordance with the following procedure. For example, assume that a single-vision lens is to be edged. When the prescription lens is determined, if it is an ordinary prescription, a corresponding prescription lens is selected from the stock lenses (mass-production products of the regular inventories).
If the prescription lens is a lens not available from the stock lenses (a custom-made article not available from the regular inventories), it is manufactured by the factory in accordance with the order. A stock lens has an upper surface (convex lens surface) and lower surface (concave lens surface) finished with predetermined lens curvatures (curves) on the basis of the optical design to have a predetermined lens power, and is completed until the final step of a surface process such as hardwearing coating or antireflection coating. Regarding a custom-made article, a lens material for it is prepared in advance in the form of a semifinished product (semifinished lens blank). The lens material is subjected to roughing-out, polishing, and the like in accordance with the ordered prescription power, and then to a surface process, so it is used as the prescription lens.
Once a prescription lens is manufactured, it is horizontally stored in a lens storing tray, together with a processing instruction slip, with its concave lens surface facing down, and is conveyed to an edging line. The operator takes out this prescription lens from the tray, places it on the inspection table of a predetermined inspecting unit such as a lens meter to check its lens power, cylinder axis, and the like. A processing center, the mounting angle of a processing jig (lens holder) with respect to the lens, and the like (optical layout) are determined from the lens information, lens frame shape data, and prescription data about a wearer. On the basis of this information, the lens holder is mounted to the processing center of the lens (blocking). The lens holder is mounted on an edger together with the lens. The lens is edged by a grind stone or cutter, thereby processing the lens into a shape conforming to the shape of an eyeglass frame.
Conventionally, an optical layout and blocking for a lens, which are included in the pre-process for edging of the lens, are manually performed by an operator using specialized devices. This process is very inefficient and low in productivity, and hence becomes a serious hindrance to labor savings. In addition, since an operator must handle the lens with great care so as not to soil, damage, and break it, a significant burden is imposed on the operator. Also, when a lens holder with a lens holding surface conforming to the curvature of the prescription lens is to be selected, the operator tends to erroneously select a different type of lens holder easily. When the operator adheres an elastic seal to the lens holder, the urging force varies, and defective adhesion occurs.
For these reasons, demands have recently arisen for the development of an apparatus for single-vision lenses, and progressive multifocal lenses and multifocal lenses (ABS; Auto Blocker for Single Vision Lens, and ABM; Auto Blocker for Multi-focus Lens), which is designed to automatically perform an optical layout for a lens and lens blocking with a lens holder, thereby improving operation efficiency. This apparatus will be referred to as a layout blocker hereinafter.
As the lens holder used for edging of the spectacle lens, for example, one disclosed in, e.g., Japanese Utility Model Laid-Open No. 6-024852 and Japanese Patent Laid-Open No. 9-225798, are known. Such a lens holder is usually formed of a cylindrical body and has a concave spherical lens holding surface at its distal end face. When holding a lens, a thin elastic seal is adhered to the lens holding surface in advance, and is urged against the convex lens surface of the lens so as to be adhered to it. The lens holding surface has a large number of fine projections, each with a triangular section, radially formed on its entire edge, so that the tight bonding properties between the lens surface and elastic seal is increased and rotation of the elastic seal is prevented.
When a lens is mounted on a conventionally known lens holder, it is then mounted on an edging device together with the lens holder. The edge of the lens is edged by a grind stone or cutter, thereby processing the lens into a shape conforming to the shape of an eyeglass frame. When performing edging, the lens holder that holds the lens is mounted on one of two coaxial clamp shafts. The two surfaces of the lens are clamped by the lens holder and the other clamp shaft. The two clamp shafts are rotated in one direction, and are simultaneously controlled, on the basis of the lens frame shape data, to move in a direction perpendicular to the axis. Edging is thus performed with the grind stone or cutter.
The lens types are infinite since one lens power D (diopter) can be combined with convex and concave surface curves, and are actually determined considering the optical aberration and inventory management. More specifically, a lens design in which the number of types of convex surface curves is decreased while different concave surface curves are used is employed. For example, regarding a progressive multifocal lens, up to 8 types of lenses, ranging from a 2-curve lens to 9-curve lens, may be prepared. In the case of a single-vision lens, as it generally copes with a wide range of power, for example, 12 types of lenses, ranging from 0-curve lens to 11-curve lens, are sometimes prepared.
The lens power D (Diopter) is expressed by a difference in curvature between a convex surface curve D1 and a concave surface curve D2. In the semi-finished lenses such as single-vision lenses or progressive multifocal lenses, their lens powers are classified in accordance with only the convex surface curves D1. For example, a single-vision lens with a convex-surface lens power D of 4 is called a 4-curve lens, and its radius of curvature is calculated by D=(N−1)×1000/R (mm) where N is the refractive index of the lens, which is 1.50 when the lens material is diethyleneglycol bis allylcarbonate, which is used most generally, and R is the radius of curvature of the convex lens surface. Hence, in the case of a 4-curve lens, when this value is substituted in the above equation, 4=(1.5−1)×1000/R yields R=125 mm. Similarly, in the case of a 7-curve lens, it is converted into a radius of curvature of about 71 mm. In the case of an 11-curve lens, its radius of curvature is about 45 mm.
Conventionally, as the lens holders, to enable stable holding, specially prepared lens holders are used for individual lenses with different lens powers, respectively, or two types of lens holders, i.e., one for a shallow curve and one for a deep curve, are used. When several types of lens holders having lens holding surfaces with different curvatures are prepared and are to be selectively used in accordance with the curvature of the convex lens surface of the lens to be held, the number of types of holders themselves increases, imposing problems in maintaining and managing them. With the method of using the two types of holders, i.e., one for the shallow curve and one for the deep curve, a flexible material (e.g., plastic) is used as the material of the holders themselves. Plastic, however, has a problem in its durability and precision. All the lens holders need be fabricated with the same size regardless of the curvatures of their lens holding surfaces. Conventionally, the types of the holders are discriminated from identification symbols or numbers formed on the outer surfaces of the lens holders by engraving or the like. In this case, the operator must form the identification symbols or numbers by engraving or the like. This operation is cumbersome. The operator must check the lens holder by manually holding it. Moreover, if the identification symbol or number becomes unclear due to the soil and wear of the surface of the holder itself, defective engraving, or the like, it is difficult for the operator to read it. Therefore, the operator must handle the lens holder carefully. In particular, when this identification method is applied to the layout blocker described above, the operator and sensor must be able to discriminate the type of the lens holder easily and reliably.
In any case, in a layout blocking step before performing conventional lens edging, various types of operation steps must be performed by the operator. These operations must be performed in a limited space, resulting in a very poor operation efficiency.